Annual bluegrass (Poa annua L.) is found on every continent and is recognized as one of the five most widespread weeds of the world. It is the only grass listed in the top five weeds. The great genetic variation in the species enables broad adaptability to a wide range of habitats. The species is most often found on sports turf fields, including golf fields. However, grounds keepers for most sports fields consider Poa annua as a pernicious and invasive weed because of variability in plant type and susceptibility to diseases, stress, and damage. They typically mount programs to eradicate it or at least discourage its growth. Sport turfgrass managers typically consider Poa annua a weed because of its characteristic light color, its profuse, year-round flowering habit, and its susceptibility to factors including heat, drought, disease, and low temperature. These criticisms are most valid in areas with high summer temperatures where Poa annua behaves as a true annual. However, the sport groundskeeper also must contend with semi-perennial types of Poa annua which prosper under conditions of moist soil, cool temperate climate, high levels of soil nutrients, and frequent close mowing. Under such conditions, the groundskeeper is up against a nemesis that propagates extensively and maintains a prolific seed bank. In addition, wild biotypes are very susceptible to many fungal diseases.
There is a considerable industry focused on the control, suppression, and eradication of Poa annua on golf courses, in sod fields, and at times on athletic fields and lawns. At least 16 states list it as a noxious weed. As a result of this listing, grass seed contaminated with the seed of Poa annua cannot be sold in many states.
There are several reasons why Poa annua as a species is considered a weed. It is often described as flowering profusely and continuously throughout the growing season. This is in part because many ecotypes of Poa annua do not exhibit day length or vernalization requirements for flowering. An additional shortcoming of the wild biotypes is that the annual type is particularly susceptible to freeze damage when its crowns are hydrated. Not only is the wild-type Poa annua intolerant of wet freezing conditions, but it is also very susceptible to damage by heat and drought stress.
The wild ecotypes possess characteristics that make a plant noxious and weed-like. However, in the right combination, some of these characteristics can be beneficial for producing a desirable variant. Poa annua is present in variable populations with a nearly endless array of genotypes ranging from annual to perennial. Hence, there is a wide genetic base of materials from which desirable cultivars may be produced. In addition, the species, as a whole, is tolerant of shade and poorly aerated soil conditions, including compaction and excessive water. Most of the wild types exhibit no seed dormancy or after ripening requirements, so seed is readily available to produce new plants. In addition, Poa annua seeds are known to remain viable for many years.
A botanical variety, Poa annua reptans, is a perennial often having a spreading habit with the potential for developing cultivars that would produce a uniform dense perennial turf. It is generally stoloniferous and propagates in the field by rooting at nodes on stolons, as well as by seed. Many of its characteristics are complementary to those of the annual variety of Poa annua. For example, Poa annua reptans can exhibit either daylength or vernalization (cold treatment) or both requirements for flowering. Poa annua reptans can exhibit seed dormancy or after ripening. However, many Poa annua reptans can tolerate heat, drought, shade, and low aeration (excessive moisture or compaction), 1/8" height of cut, and possess other desirable traits.
Some individual biotypes of Poa annua possess desirable turfgrass characteristics for golfing applications. As an unwanted invader of bentgrass greens, Poa annua can, under certain conditions, be cultivated and bred to produce an acceptable turf and putting surface. However, the broad expression of phenotypic variation in color, growth rate, habit of growth, flowering habit, and susceptibility to disease and stress damage make Poa annua undesirable despite its tolerance of low (1/8) height of cut and poor soil conditions.
Poa annua can seed prodigiously and injured areas can eventually recover from seed. On these bases, Poa annua is unreliable and is despised by turf managers because it often fails suddenly at critical times during the growing season. Typically, this failure results from high susceptibility to disease and low heat or cold tolerance and the normal completion of the annual growth cycle.
Cultivars of Poa annua, particularly of perennial types, with desired restricted flowering habit, have not been previously available.
Hence, there is a need for uniform, reliable variety of Poa annua with characteristics of a desirable turfgrass for sports fields, particularly golf courses. There is a need for a Poa annua variety and seed that provides a uniform population with desirable traits, that is a dense turf having a uniform, dark green color, restricted flowering habit, and good performance at moderate to low fertility. Such varieties of Poa annua will also have characteristics that will enable them to tolerate the low mowing, disease exposure, and traffic conditions of a golf course or other sporting field.